1. Teosinte derivatives. Additional studies to determine the linkage relations of the blocks of genes, or chromosome segments, which distinguish teosinte from maize are, in general, in agreement with the results reported in the 1947 Maize News Letter. In teosinte derivatives which contain two or more segments, one of the segments is almost invariably that on chromosome 4. There is no doubt that the segment on chromosome 4 is the most conspicuous of all the segments in its effects and is almost certain to be included in derivatives which exhibit strong teosinte effects.

The data from the 1947 tests are shown in table 1. Considered in connection with last year's data they show that the principal segments in Florida and Durango are located on chromosomes 1,3,4, and 9; in "New" teosinte on 3 and 4, and probably 1 and 9; and in Nobogame teosinte on 3 and 4, and probably 1.

The only data not in obvious agreement with the conclusions are the 1947 data on the derivatives from Durango teosinte which show a definite linkage with the marker gene on chromosome 10 in one cross and indications of linkage on chromosomes 2,6, and 7. These partiaular teosinte derivatives are descendants of an F₂ plant, however, rather than the result of repeated backcrossing L an inbred strain of maize. Hence, small segments or modifying factors on chromosomes other than 1,3,4, and 9 may be playing a part. Linkage relations of the characteristics which distinguish Durango teosinte from maize, as determined from F₂ populations, reported here in 1945, indicate that chromosomes 2,3,4,6,8,9, and 10 are involved. Teosinte apparently differs from maize primarily by three or four chromosome segments which involve chromosomes 1,3,4, and 9, but there are small segments, not easily detectable, or modifying factors on most or all of the remaining chromosomes.

That the chromosome segments from teosinte are transmitted in inheritance as definite and stable entities is shown by "New" teosinte progenies 1205 and 1156.These were derived from a single plant in 1940 but have had separate lines of descent since that time. When these progenies were recently tested for linkage relations, chromosomes 3 and 4 were shown to be involved in both.

We also have one instance involving data presented last year, in which two stocks, each apparently carrying one segment, were crossed, to produce a stock carrying both segments. When the three different stocks were tested to determine the linkage relations of the segments, it was found that one parental stock involved chromosome 3, the other chromosome 4, and their two-segment derivative involved chromosomes 3 and 4.

Table 1. Linkage relations of teosinte segments

Pedigree number	Variety of teosinte	Number of segments	Linkage with chromosome number									Total number chromosomes tested
			1	2	3	4	6	7	8	9	10
1195	Florida	1	-	-	-	+	-	-	-	-	-	450
1149	"	2	-	-	+	+	-	-	-	-	-	702
962	Durango	2	-	I	-	+	-	-	-	I	-	531
1151	"	2	-	I	-	+	-	-	-	I	-	621
963	"	2-3	-	I	I	+	-	-	-	-	-	657
1152	"	2-3	+	-	-	-	-	I	-	+	-	603
1153	"	2-3	I	-	-	+	I	I	-	+	+	1593
1206	New	1	I	-	-	-	-	-	-	-	-	1620
1205	"	2	-	-	+	+	-	-	-	-	-	1494
1156	"	2	-	-	+	+	-	-	-	-	-	1656
1154	Nobogame	2	-	-	+	+	-	-	-	-	-	1449
1155	"	2	+	-	-	+	-	I	-	-	-	1080
1207	"	2	-	-	+	+	-	-	-	-	-	1566

+ = Linkage

I = Indication of linkage

- = Independent inheritance